The present invention relates generally to methods and apparatus for connecting lengths of coiled tubing. More particularly, the present invention relates to spoolable coiled tubing connectors that maintain the pressure and tensile strength ratings of the tubing.
Conventional tubing strings are constructed in thirty foot long straight sections that are connected in series. A coiled tubing string generally includes a continuous length of small diameter tubing that is much more flexible than conventional tubing and can therefore be spooled onto a reel. The coiled tubing is unwound from the reel and directed over a gooseneck and through a tubing injector head into a wellbore. Coiled tubing is used for a variety of wellbore processes, including injecting gas or other fluids into the wellbore, inflating or activating bridge plugs and packers, transporting well logging tools downhole, performing remedial cementing and clean-out operations in the wellbore, and delivering or retrieving drilling tools downhole.
As the utilization of coiled tubing expands into applications involving greater depths, pressures, and more remote operating locations, the complexity and size of a coiled tubing system increase. Transportation and handling constraints often limit the size of the reel and the corresponding length of coiled tubing able to be stored on a given reel. To overcome this limitation, lengths of coiled tubing from multiple reels can be connected in series and used in a single operation. These multiple lengths can then be spooled back onto a single, larger reel for more efficient storage. Although lengths of coiled tubing can be welded together, welding requires special equipment, personnel, and a closely controlled environment. In connecting lengths of coiled tubing, a mechanical connector that does not require welding at a well site can simplify the connection process by enabling faster connections in a wider variety of environmental conditions.
In operation, coiled tubing is subjected to bending stresses both when being spooled onto and off of the reel and when being fed over the gooseneck into the injector head. A mechanical connector joining lengths of coiled tubing will also be subjected to these bending stresses. As the length and stiffness of a connector increase, areas of stress concentration will develop in the regions of the coiled tubing immediately adjacent to the connector. Therefore, it is desirable to minimize both the overall length and stiffness of a coiled tubing connector.
Thus, there remains a need to develop methods and apparatus for connecting lengths of coiled tubing, which overcome some of the foregoing difficulties while providing more advantageous overall results.